Start circuit for dc motor having a thyristor commutator

ABSTRACT

When firing or ignition transformers are utilized in the firing or ignition circuit of an electronic commutator such as, for example, that utilized in the Siemotron drive, there is no ignition or firing pulse at the thyristors during the start of the motor due to the signal provided by the rotor position sensor. In order to insure a reliable start of the motor, additional firing pulses are periodically applied to the firing circuit. Upon the attainment of a specific speed, the additional pulses are automatically discontinued.

United States Patent 1 1 1 ,69 ,2

I 3,517,289 6/1970 Brunner et al. ..318/254 X Liska et al. 1 1 Oct. 3,1972 4] START CIRCUIT FOR DC MOTOR 3,518,516 6/1970 Pawletko ..318/138HAVING A THYRISTOR 3,319,104 5/1967 Yasuoka et al. ..318/138CONHVIUTATQR 3,412,303 11/1968 Raues ..318/138 Inventors: Manfred LiskaKlaus Hume}, both 2,814,769 11/1957 Williams ..318/ 138 3,402,337 9/1968Malmborg et al. ..318/254 ofMumchGermany 3,242,406 3/1966 Tanaka..318/138 [73] Assignee: Siemens Aktiengesellschaft, Berlin and MunichGel-many Pnmary Exammer-G. R. Sunmons Attorney-Curt M. Avery, Arthur E.W11fond, Herbert [22] Filed: Oct. 29, 1970 L. Lerner and Daniel J. Tick[21] Appl.No.: 85,119 1 [57] ABSTRACT [30] Forelgn Apphcatlon Prwmy DataWhen firing or ignition transformers are utilized in the Oct. 31, 1969 Gr P 19 54 3461) firing or ignition circuit of an electronic commutatorsuch as, for example, that utilized in the Siemotron 52 U.S. c1...318/138,318/254,318/439 drive, there is he ignition or firing pulse atthe 51 1m. (:1 ..F02n 11/00 thyriswrs during the Start of the meter dueto the [58] Field 61 Search ..318/138, 254, 696, 685, 439 signalProvided the rotor Position senSOf- Order to insure a reliable start ofthe motor, additional firing 5 References Cited pulses are periodicallyapplied to the firing circuit.

- Upon the attainmentof a specific speed, the addi- UNITED STATESPATENTS tional pulses are automatically discontinued. 3,488,566 1/1970Fukuda ..318/254X 10 Claims, 5 Drawing Figures 11 22a 57a r211.111111111 11111 21 28a SPEED 12 nssuumn 1 1 37 l PULSE L35.s1111nA1on-- 33 1L 9 FIRST DIFFERENIIATUR n-x SECOND MULTIPLIER /SECUNUDIFFERENTIAT 11R START CIRCUIT FOR DC MOTOR HAVING A THYRISTORCOMMUTATOR The invention relates to a start circuit for a DC motorhaving a thyristor commutator. More particularly, the invention relatesto a start circuit for a DC motor having a thyristor commutator, thethyristors of which are conductively controlled in accordance with theposition of the motor rotor, via firing or ignition transformers ofswitching transistors.

In a thyristor commutator of the type described herein, a thyristor isconnected in series with a winding of the motor and is connected to asource of direct voltage. The thyristor is conductively controlledduring the position of the rotor of the motor at which the windingproduces a maximum torque with the magnetic field, analogously to themode of operation of a known commutator utilizing brushes.

The firing or ignition pulses for the thyristors of the commutator arederived in commutators of the type of the invention from the outputsignals of a rotor position sensor or indicator. Since, due to thenecessary galvanic separation, firing or ignition transformers mustusually be utilized, the firing pulses may be provided only duringsignal changes of the rotor position sensor, that is, when the motor isrotating during a planned motor start, from standstill, .no firingpulses for the thyristors of the commutator may. be produced by thecontinuous or constant signal which is then provided at the output ofthe rotor position sensor. It is thus not easy to start the motorwithout difficulties.

The principal object of the invention is to provide a new and improvedstart circuit for a DC motor having a thyristor commutator.

An object of the invention is to provide a start circuit for a DC motorhaving a thyristor commutator, which overcomes the disadvantages ofknown types of thyristor commutators.

An object of the invention is to provide a start circuit for a DC motorhaving a thyristor commutator, which permits easy starting of the motorwithout difficulty.

An object of the invention is to provide a start circuit for a DC motorhaving a thyristor commutator, which functions with efficiency,effectiveness and reliability.

In accordance with the invention, the disadvantages of known types ofthyristor commutators are overcome by the provision of a pulse generatorwhich produces additional control pulses for the switching transistors.The additional firing pulses for the thyristors of the commutator may beprovided in a simple manner, by superimposing the output voltages of thepulse generator on the individual control voltages for the inputtransistors. The collector electrodes of the input transistors areconnected to the control paths of the switching transistors. Inaccordance with another aspect of the invention, it is expedient todisconnect the output voltage of the pulse generator in accordance withthe speed of the motor by means of a limit or threshold circuit whichcontrols a switch. This results in very quiet running of the motor athigher speed.

A rotor position sensor, which is usually a sine-cosine sensor, isprovided for energizing the individual windings of the motor inaccordance with the position of the rotor of said motor. Therefore, thesignal which is proportional to the speed of the motor, which isrequired for the automatic discontinuation of the additional controlpulses, is preferably provided with the assistance of a static speedindicator. The output of the speed indicator is connected to the limitor threshold circuit. The speed indicator comprises first and seconddifferentiators. The first difierentiator is connected in series circuitarrangement with a first multiplier and the second differentiator isconnected in series circuit arrangement with a second multiplier. Theoutput voltages of the first and second multipliers are subtractivelyapplied to an adding amplifier. Each of the two output voltages of thesine-cosine sensor, which sensor is coupled to the shaft of the motor,is applied to the input of a corresponding one of the differentiatorsand the input of a corresponding one of the multipliers. The multipli- Ier to which each input is applied is not that which is connected inseries circuit arrangement with the differentiator to which the sameinput is applied.

If the DC motor is energized by the output of a controlled rectifier orthyristor, the synchronizing part of the rectifier control unit may beutilized as a pulse generator.

In accordance with another embodiment of the invention, the additionalfiring or ignition pulses may be provided in a manner whereby thecontrol paths of the switching transistors are energized by thecollector potential of the corresponding input transistors. The inputtransistors are connected in parallel, in common, with a transistorswitch located at the output of the pulse generator. The pulse generatormay be provided, in a simple manner, with a charging capacitor which isconnected via a resistor to a source of direct voltage. The chargingcapacitor has a discharge current path in which is connected a doublebase diode which may be fired or switched to its conductive condition bythe capacitor voltage.

An economical embodiment for automatically discontinuing the operationof the timer, when the motor speed is higher, comprises connecting thebase electrodes of the switching transistors with the collectorelectrodes of the corresponding input transistors via correspondingcapacitors and connecting the collectoremitter paths of the switchingtransistors in parallel with the corresponding charging capacitors viacorresponding decoupling diodesThe coupling of the collector'electrodeof each input transistor to the base electrode of the correspondingswitching transistor via a capacitor prevents unnecessary dissipation orconsumption of the control current during the standstill of the motor.

In accordance with the invention, a start circuit for a DC motor havinga rotor, a thyristor commutator comprising a plurality of thyristors andfiring circuit means coupled to the rotor of the motor and connected tothe thyristors for conductively controlling the thyristors with controlpulses in accordance with the position of the rotor of the motor, thefiring circuit means including a plurality of firing transformers eachconnected to a corresponding one of the thyristors, a plurality ofswitching transistors each connected to a corresponding one of thefiring transformers and control means coupled to the rotor of the motorand connected to the switching transistors for supplying control pulsesto the switching transistors, comprises a pulse generator connected tothe switching transistors of the firing circuits for providingadditional control pulses for the switching transistors. Each of theswitching transistors of the firing circuit means has a control path andthe firing circuit means further comprises a plurality of inputtransistors each having a collector electrode connected to the controlpath ofa corresponding one of said switching transistors and a baseelectrodeconnected to the pulse generator whereby the additional controlpulses provided by the pulse generator are superimposed upon the controlpulses supplied to the switching transistors via the input transistors.

In one embodiment of the invention, the pulse generator includes aswitch for controlling the output of the additional controlpulses and alimit circuit coupled to the rotor of the motor and controlling theoperation of the-switch for discontinuing the output of the additionalcontrol pulses from the pulse generator via the switch in accordancewith therotary speed of the motor.

A sine-cosine sensor has a pair of inputs coupled to the rotor of themotor and pair of outputs and speed indicating means has inputs coupledto the outputs of the sine-cosine sensor and an output connected to thelimit circuit of the pulse generator. The speed indicating meanscomprises a first differentiator having an input connected to one of theinputs, a first multiplier having an input connected in series circuitarrangement with the first differentiator, another input connected toanother of the inputs and an output, a second differentiat or having aninput connected to the other of the inputs, a second multiplier havingan input connected in series circuit arrangement with the seconddifferentiator, another input connected to the first of the inputs andan output, and summing means having an output connected to the limitcircuit of the pulse generator, an input connected to the output of thefirst multiplier and another input connected to the output of the secondmultiplier for subtractively combining output signals from the first andsecond multipliers.

Motor energizing means connected between the output of the speedindicating means and the thyristors of the thyristor commutator includesrectifier means connected to the thyristors and a rectifier control unitconnected to the rectifier means and having a synchronizing stageconnected to the pulse generator for energizing the pulse generator.

In another embodiment of the invention, the pulse generator comprises aswitching transistor connected as the output stage thereof and connectedin parallel to the collector electrode of each of the input transistorsand the control path of each of the switching transistors is energizedby the collector potential of the corresponding input transistor. Thepulse generator comprises a source of direct voltage, a chargingcapacitor and a resistor connected in series circuit arrangement withthe charging capacitor to the source of direct voltage, a dischargecurrent path connected to a common point in the connection between thecharging capacitor and the resistor, and a switching transistorconnected as the output stage of the pulse generator and connected inparallel to the collector electrode of each of the input transistors.

The discharge current'path of the pulse generator comprises a doublebase diode which is fired by the voltage of the charging capacitor.

Each of the switching transistors has a base electrode and anemitter-collector path and the firing circuit means further comprises aplurality of capacitors each connected between the collector electrodeof a corresponding one of the input transistors and the base electrodeof a corresponding one of the switching transistors, and a plurality ofdecoupling diodes each connected between the charging capacitor of thepulse generator and the emitter-collector -path of a corresponding oneof the switching transistors. I

In order that the invention may be readily carrie into effect, it willnow be described with reference to the accompanying drawings, wherein:

FIG. 1 is a block diagram of an embodiment of the start circuit of theinvention;

FIG. 2 is a block diagram of an embodiment of the selector circuit ofFIGS. 1, 4 and 5;

FIG. 3 is a graphical presentation of the variousvoltages appearing inthe selector circuit of FIG. 2;

FIG. 4 is a block diagram, including a partial circuit diagram, ofanother embodiment of the start circuit of the invention; and

FIG. 5 is a block diagram, including a partial circuit diagram, of stillanother embodiment of the start circuit of the invention.

In the FIGS., the same components are identified by the same referencenumerals.

FIG. 1 illustrates a speed controlled DC motor having an electroniccommutator comprising four thyristors 1, 2, 3 .and 4. The motor andthyristors are not shown in any of the other FIGS., although each of Thesine-cosine sensor 6 comprises a permanent disc magnet having a pair ofmagnetic poles N and S and first and second Hall probes 7a and 7bmutually displaced by a peripheral angle of The first Hall probe 7a hasan output terminal 8 and the second Hall probe 7b has an output terminal9.

The first Hall probe 7a produces at its output terminal 8 a voltagewhich is proportional to the sine of the angle of rotation a of themotor. The second Hall probe 7b produces at its output terminal 9 avoltage which is proportional to the cosine of the angle of rotation aof the motor. The sine-proportional voltage and the cosine-proportionalvoltage are applied to the inputs of a selector circuit 10. Thepermanent magnet disc of the sine-cosine sensor 6 may, of course, beeliminated; In such case, the Hall probes 7a and 7b may be positioned orlocated at the stator circumference of the DC motor in a suitablemanner.

The selector circuit 10 functions to prepare a pulse during each quarterrotation of the rotor 5 of the motor. The pulse provided by the selectorcircuit 10 initiates the energization of that one of the four motorwindings W1, W2, w3 and w4 which provides the maximum'torque with therotating magnetic field of the rotor.

' The voltage which is proportional to the sine of the angle of rotationof the motor and the voltage which is proportional to the cosine of theangle of rotation of the motor are also applied to input terminals 11and 12 of a static speed indicator 13. The speed indicator 13 provides,at an output terminal 14, a voltage proportional to the magnitude whichvoltage is proportional to the motor speed n. The output voltage of thespeed indicator 13 functions as the actual speed value n and is appliedto an input of a speed regulator 20. A voltage which functions as thedesired datum or reference value n* is applied to the other input of thespeed regulator 20.

The speed indicator 13 comprises a first differentiator 15, a seconddifferentiator 16, a first multiplier 17 and a second multiplier 18. Thefirst multiplier 17 is connected in series circuit arrangement with thefirst differentiator 15. The second multiplier 18 is connected in seriescircuit arrangement with the second differentiator 16. The inputterminal 11 of the speed indicator 13 is connected to the input of thefirst differentiator 1S and to an input of the second multiplier 18. Theinput terminal 12 if the speed indicator 13 is connected to the input ofthe second differentiator 16 and to an input of the first multiplier 17.The output voltages of the first and second multipliers 17 and 18 aresubtractively applied to an adding amplifier 19 or other suitable meansfor combining said output voltages.

Due to the differentiating effect of the first differentiator 15, saiddifferentiator produces an output voltage proportional to the magnitude1 6: sin a and the second differentiator 16 produces an output voltageproportional to the magnitude 6: cos a.

The output voltage of the speed indicator 13, which appears at theoutput terminal 14, thus corresponds to the rotor speed n of the motor.A magnitude proportional to the rotor speed of the motor may also beprovided, in

a known manner, by the utilization of a tachometer.

The output signal or voltage of the speed regulator 20 triggers acontrol unit 21, which comprises a known circuit arrangement for thefiring or ignition of two thyristors 22a and 22b. The thyristors 22a and22b are connected in a bridge circuit 23 energized by an AC power supplyvoltage U. Of the four rectifiers of the bridge circuit, only thethyristors 22a and 22b are controlled rectifiers. A zero anode isconnected to the bridge circuit 23 in order to relieve the power supplysystem. The direct current provided by the bridge circuit 23 via asmoothing reactor or inductor 24, and thus the torque of the motor,varies in accordance with the control rate of the thyristors 22a and 22bof said bridge circuit. This continues until the datum or referencemagnitude of the speed of the motor and the actual magnitude of thespeed of said motor are the same.

The firing or ignition pulses of the thyristors 1, 2, 3 and 4 of thecommutator are provided by secondary windings of firing or ignitiontransformers included in a plurality of firing or ignition circuits 25,.26, 27 and 28. The firing circuit 25 includes a firing transformerhaving a secondary winding 25a. The secondary winding 25a is connectedto the control electrode of the thyristor l. The firing circuit 26includes a firing transformer having a secondary winding 26a. Thesecondary winding 26a is connected to the control electrode of thethyristor 2. The firing circuit 27 includes a firing transformer havinga secondary winding 27a. The

secondary winding 27a is connected to the control electrode of thethyristor 3. The firing circuit 28 includes a firing transformer havinga secondary winding 28a. The secondary winding 28a is connected to thecontrol electrode of the thyristor 4.

The triggering pulses required to trigger, fire, ignite, or switch totheir conductive condition, the thyristors l, 2, 3 and 4, are derivedfrom the output pulses of the selector circuit 10. The selector circuit10 has a plurality of output terminals 29, 30, 31 and 32. Each of theoutput terminals 29, 30, 31 and 32 of the selector circuit 10 functionsas an input terminal of a corresponding one of the firing circuits 25,26, 27 and 28. The firing or ignition transformers of the firingcircuits 25, 26, 27 and 28 can only provide voltage pulses, but not DCvoltage. It is therefore necessary that a cyclic signal variation shouldoccur continuously or constantly at the input terminals 29, 30, 31 and32 in order to maintain continuous or constant ignition or firing of thethyristors. When the motor is at standstill, however, a purely directvoltage is provided at the output terminals 8 and 9 of the Hall probes7a and 7b, and, therefore, also at the output terminals of the selectorcircuit 10.

In accordance with the invention, apulse generator 33 is provided. Thepulsegenerator 33 produces periodic supplemental pulses. The outputpulses produced by the pulse generator 33 are applied to the inputterminals 29, 30, 31 and 32 of the firing circuits 25, 26, 27 and 28,respectively. The selector circuit 10 controls the firing of thecorresponding thyristors l to 4 of the commutator via the inputterminals 29 to 32 only for specific rotor positions of the motor.

Asindicated in broken lines in FIG. 1, the energizing voltage of thepulse generator 33 may be provided by the synchronization stage orcircuit of the control unit 21, thereby eliminating the need for aseparate oscillator. Such an energizing voltage may be applied via aninput terminal 34 of the pulse generator 33. The pulse generator 33 hasanother input terminal 35, which is connected to the output terminal 14of the speed indicator 13. Thus, when the motor reaches a specificspeed, a command signal may be sent to the pulse generator 33 todiscontinue the supply of additional control pulses.

The additional control or firing pulses provided by the pulse generator33 are superimposed upon the pulses provided by the selector circuit 10at the input terminals 29, 30, 31 and 32 of the firing circuits 25, 26,27 and 28, respectively. Instead of providing the additional firingpulses at the input terminals 29 to 32, a pulse generator 36 may beprovided. The pulse generator 36 comprises a transistor switch 37 whichis energized by an oscillator. The transistor switch 37 has a collectorelectrode connected in common to a plurality of-input terminals 38, 39,40 and 41 of the firing or ignition circuits 25, 26, 27 and 28.

The supply of the additional firing pulses produced by the pulsegenerator 36 to the firing circuits 25 to 28 via the input terminals 38to 41, respectively, insures the provision of additional firing pulsesfor corresponding ones of the thyristors 1, 2, 3 and 4, in accordancewith the rotation of the rotor of the motor. The pulse generator 36 hasan input terminal 42. A signal may be derived from the firing circuits25, 26, 27 and 28 and applied to the input terminal 42 of the pulsegenerator 36 to additionally energize the transistor switch 37 thereofafter a specific firing'or ignition frequency has been provided, thatis, starting with a specificmotor speed.

FIG. 2 illustrates a selector circuit which may be utilized as theselector circuit of FIGS. 1, 4 and 5. The selector circuit 10 has inputterminals 8 and 9 and output terminals 29, 30, 31 and 32, as in FIG. 1.The input of a limit or threshold circuit 43 is connected to the inputterminal 9. The input of a limit or threshold circuit 44 is connected tothe input terminal 8. The first Hall probe 7a FIG. 1 supplies a voltageproportional to the sine of the angle of rotation at of therotor of themotor to the input terminal 8. The second Hall probe 7b (FIG. 1)supplied a voltage proportional to the cosine of the angle of rotationat of the rotor of the motor to the input terminal 9.

At positive magnitudes of the voltages applied to the input terminals 8and 9, a constant positive voltage or signal is provided at the output aof the limit circuit 43 and at the output b of the limit circuit 44. Theoutput a of the limit circuit 43 is connected to an input of an AND gate45 and to an input of an OR gate 46. The output b of the limit circuit44 is connected to the second input of the AND gate 45, the second inputof the OR gate 46 and a first input of an AND gate 47. The AND gate 45has an output c connected to a second input of the ANDgate 47, a firstinput of an AND gate 48 and the output terminal 30. The OR gate 46 hasan output d connected to the third input of the AND gate 47, a secondinput of the AND gate 48 and the output terminal 32.

The AND gate 47 has an output e connected to the third input of the ANDgate 48 and the output terminal 31. The AND gate 48 has an output fconnected to the output terminal 29. The inputs of the AND gate 47 arethus energized by outputs b, c and d.

FIG. 3 illustrates the pulses or signals occurring at the outputs c, d,e and f of the selector circuit 10 of FIG. 2 and at the outputs of thelimit circuits 43 and 44 of said selector circuit. The pulses areprovided for a motor which rotates at a rotary or angular speed of Thetime T is the period of rotation of a single revolution of the rotor.When the output terminals 29 to 32 of the selector circuit 10 coincidewith the input terminals of the firing circuits 25 to 28, respectively,a zero signal continuously appears at said terminals in a sequencedepending upon one quarter revolution of the rotor of the motor.

In FIG. 3, the abscissa represents the time t and the ordinaterepresents the voltage V. The onset of the zero signal may be utilized,at time instants Z1, Z2, Z3 and Z4, to cyclically trigger the thyristors1, 2, 3 and 4 of the commutator. When the motor is at standstill, a zerosignal constantly occurs at one of the terminals 29, 30, 31 and 32,while the others of said terminals have a positive potential.

In the embodiment of FIG. 4, additional trigger, firing, ignition, orthe like, pulses are superimposed on the pulses from the selectorcircuit 10 at the input terminals 29, 30, 31 and 32 of the firing orignition circuits 25, 26, 27 and 28, respectively. In the embodiment ofFIG. 4, each of the firing circuits 25, 26, 27 and 28 '8 comprises anidentical circuit. However, in order to maintain the clarity ofillustration, the circuit of only the firing circuit 25 is illustrated.The firing circuit 25 is, however, illustrative of the firing circuits26, 27 and 28, as well. y I

The firing circuit 25 comprises a firing transformer 49 having asecondary winding connected to the control path of the thyristor 1 ofthe commutator (FIG. 1). Thus, one end of the secondary winding of thefiring transformer 49 is connected to the control electrodeIof thethyristor 1 and the other end of said winding is connected to thecathode of said thyristor whereby said thyristor is fired, ignited'orswitched to its conductive condition, by said secondary winding. Thesecondary winding of the firing transformer of the firing circuit 26 issimilarly connected to, and similarly controls, the thyristor 2. Thesecondary winding of the firing transformer of the firing circuit 27 issimilarly connected to, and similarly controls, the thyristor 3. Thesecondary winding of the firing transformer of the firing circuit 28 issimilarly connected to, and similarly controls, the thyristor 4. I

The primary winding of the firing transformer 49 is connected in serieswith the collector-base path of a switching transistor 50 and a currentlimiting resistor 51, to a DC voltage source +U of positive polarity.The switching transistor 50 has a base electrode connected to thecollector electrode of an input transistor 52. The input transistor 52has a base electrode connected to the input terminal 29 of the firingcircuit 25.

The base electrode of the input transistor of the firing circuit 26 isconnected to the input terminal 30. The base electrode of the inputtransistor of the firing circuit 27 is connected to the input terminal31. The base electrode of the input transistor of the firing circuit 28is connected to the input terminal 32. The output voltages or signals f,c, e and d of the selector circuit 10 are applied to the input terminals29 to 32 of the firing circuits 25 to 28, respectively, via a pluralityof decoupling diodes 29a, 30a, 31a and 32a. The output voltage of anamplifier 53 is also superimposed upon the output signals f, c, e and dof the selector circuit 10 via a plurality of decoupling diodes 29b,30b, 31b and 32b. The input voltage of the amplifier 53 is a pulsevoltage applied to an input terminal 34 of said amplifier and may bederived, for example, from the synchronization stage or circuit of thecontrol unit 21 (FIG. 1).

The output signal or voltage of the amplifier 53 may be suppressed by aswitch 54, when said switch is in its open condition. The switch 54 iscontrolled by the response of a limit or threshold circuit 55. The limitcircuit 55 has an input terminal 35 to which a signal n, proportionalto' the speed of the motor, is supplied. When the input signal n to thelimit circuit 55 exceeds an assumed limit or threshold e1 or e2, theswitch 54 is opened and the output voltage of the amplifier 53disappears. The limits el and e2 are for opposite directions of rotationof the motor.

When the speed of the motor is sufficiently high, the circuit of FIG. 4operates as follows. The control signal applied to the base of the inputtransistor 52 of the firing circuit 25 and of the input transistor ofeach of the firing circuits 26, 27 and 28, changes once for eachrotation or revolution of the rotor of the motor, from a positivemagnitude to zero magnitude. The input transistor 52, and that of eachof the firing circuits 26, 27 and 28, is initially in conductivecondition, but is switched to its non-conductive condition when thecontrol signal changes from a positive magnitude to zero magnitude. Whenthe input transistor 52 is switched to its non-conductive condition, theswitching transistor 50 is switched to its conductive condition.

When the switching transistor 50 is switched to its conductivecondition, an output pulse is provided by the firing transformer 49. Theoutput pulse of the firing transformer 49 is produced in the secondarywinding thereof and switches the corresponding thyristor l of thecommutator to its conductive condition. Onequarter revolution later, thesignal at the input terminal 29 again assumes a positive potential andthe input transistor 52 is again switched to its conductive condition.When the input transistor 52 is switched to its conductive condition,the switching transistor 50 is switched to its non-conductive conditionand the firing transformer 49 becomes demagnetized and returns to itscondition of prior to the firing or ignition of the thyristor 1.

When the motor is at standstill due, for example, to the disconnectionor discontinuation of the direct voltage which energizes the thyristorsof the commutator, there is no signal change at the outputs f, c, e andd, or 29, 30, 31 and 32 of the selector circuit 10. Dependent upon theposition of the rotor of the motor, one of the switching transistors ofthe firing circuits 25, 26, 27 and 28 is switched to its conductivecondition and the corresponding firing transformer connected thereto isenergized or saturated. If the voltage which energizes the thyristors ofthe commutator is additionally applied in order to undertake a plannedstart of the motor, nothing changes in this condition, since in theabsence of firing or ignition pulses the motor cannot start.

The switch 54 of the pulse generator 33 of FIG. 4 is closed duringstandstill of the motor. Since the switch 54 is closed, the outputpulses of the amplifier 53 are provided at the input terminals 29, 30,31 and 32 of the firing circuits 25, 26, 27 and 28, respectively. Thesuperimposed additional pulses provided by the amplifier 53 may effectperiodic opening and closing of the switching transistors of the firingcircuits, and thus the production of firing pulses for the correspondingthyristors, only during the firing stage. The selector circuit providesthe zero signal to the switching transistors of the firing circuits 25to 28. Thus, the additional superimposed pulses are automaticallyapplied to the thyristor of the commutator which is intended to be firedor ignited, in accordance with the position of the rotor of the motor. Aseparate distribution circuit for the additional pulses may thus beomitted.

The motor may therefore be reliably started from standstill. When aspecific rotary or angular speed is reached by the motor, thesupplementary circuit or pulse generator 33 is discontinued in operationwith the assistance of the limit circuit 55 thereof.

FIG. 5 shows another arrangement for providing the additional controlpulses for the switching transistor 50 and the switching transistor ofeach of the firing circuits 26, 27 and 28. In FIG. 5, the circuit of thefiring circuit 25 is illustrated and those of the firing circuits 26, 27and 28 are not illustrated in the interest of maintaining the clarity ofillustration. The discussion of the firing circuit 25 applies to thefiring circuits 26, 27 and 28 as well. In the embodiment of FIG. 5, aself-oscillating multivibrator or flip flop circuit is utilized. Theadditional pulses are automatically suppressed at higher motor speeds,due to the particular design of the firing or ignition circuits. Thestructure of the firing or ignition circuits 25, 26, 27 and 28 of FIG. 5differs considerably from that of said firing circuits of FIG. 4.

The base electrode of the switching transistor 50 is coupled to thecollector electrode of the input transistor 52 via a correspondingcapacitor 56. The input transistor 52 is triggered or controlled by theselector circuit 10 in the afore-described manner. In each of the firingcircuits 26, 27 and 28, the base electrode of the switching transistoris coupled to the collector electrode of the input transistor via acorresponding capacitor. When the input transistor 52 is switched to itsnon-conductive condition, the capacitor 56 begins to charge via thecollector resistance of said transistor. The charge current of thecapacitor 56 switches the switching transistor 50 to its conductivecondition.

Upon the completion of the charging of the capacitor 56, the switchingtransistor 50 is switched to its nonconductive condition, whereupon thefiring transformer 49 commences to demagnetize and thus returns to itsinitial unenerg ized condition. The principal course of the chargecurrent of the capacitor 56, which is the charge current of thecorresponding capacitor of each of the firing circuits, is shown by thebroken lines in FIG. 3, occurring at difierent times. The charge currentof the capacitor 56 does not depend upon the speed of the motor. It isinteresting that in the circuit arrangement of FIG. 5, there is aspecific maximum feasible time range, even at low motor speeds, duringwhich the switching transistor 50 is in its conductive condition. Due tothe switching transistor 50 being in its conductive condition, a currentflows through the primary winding of the firing transformer 49. The timerange during which the switching transistor 50 is in its conductivecondition is determined by the charge time constant of the capacitor 56.

A current limiting resistance may thus be eliminated and unnecessarycontrol current losses may be avoided. After the signal at the inputterminal 29, 30, 31 or 32 of the firing circuit 25, 26, 27 or 28,respectively, changes from zero magnitude to a positive magnitude, theinput transistor of such firing circuit is switched to its conductivecondition. When the input transistor such as, for example, the inputtransistor 52 of the firing circuit 25, is switched to its conductivecondition, the capacitor such as, for example, the capacitor 56,discharges via said input transistor and via a resistor such as, forexample, the resistor 57 of the firing circuit 25. When the capacitordischarges via the corresponding input transformer and the correspondingresistor, another control pulse for the corresponding switchingtransistor such as, for example, the switching transistor 50 of thefiring circuit 25, is suppressed thereby, provided the control pulse hasnot already become zero due to the decay of the capacitor chargecurrent.

In the embodiment of FIG. 5, the pulse generator 36 comprises aself-oscillating multivibrator or flip flop circuit, a chargingcapacitor C1 and a resistor R1, connected in series to the positivepolarity terminal +U of a source of direct voltage. A double base diode58 is connected to a common point in the connection between thecapacitor C1 and the resistor R1. The double base diode 58 is switchedto its conductive condition at a specific magnitude of the chargingvoltage of the capacitor C1 when said charging voltage increases. Whenthe double base diode 58 is switched to its conductive condition, theswitching transistor 37, connected to said double base diode, isswitched to its conductive condition. The switching transistor 37remains in its conductive condition for the duration of the discharge ofthe capacitor C1 via the double base diode 58. When the voltage of thecapacitor C1 increases, the double base diode 58 and the switchingtransistor 37 are switched to their non-conductive condition. Thecapacitor C1 then charges.

The switching transistor 37 is connected at the output stage of thepulse generator 36 of the embodiment of FIG. The switching transistor 37is connected in parallel with an input terminal 38 of the firing circuit25, an input terminal 39 of the firing circuit 26, an input terminal 40of the firing circuit 27 and an input terminal 41 of the firing circuit28. The input terminal 38 is coupled to the collector electrode of theinput transistor 52.0f the firing circuit 25. Each of the inputterminals 39, 40 and 41 is similarly coupled to the collector electrodeof the corresponding input transistor of the firing circuits 26, 27 and28, respectively.

The periodic switching of the switching transistor 37 of the pulsegenerator 36 to its conductive and nonconductive condition may produce afiring or ignition pulse only in that firing circuit, the inputtransistor of which is switched to its non-conductive condition by anoutput signal of the selector circuit 10. This is due to the fact thatthe periodic opening and closing of a switch connected in parallel witha closed switch cannot create an additional effect. Thus, only thatthyristor of the commutator which is desired to be fired or ignited issupplied with additional firing pulses.

The automatic suppression of the additional pulses in the embodiment ofFIG. 5 results from the provision of a decoupling diode 60 in the firingcircuit 25 and a corresponding decoupling diode in each of the firingcircuits 26, 27 and 28. The collector electrode of the switchingtransistor 50 is coupled to the charging capacitor C1 of themultivibrator circuit via the decoupling diode 60. The chargingcapacitor C1 of the multivibrator is coupled to the collector electrodeof the switching transistor of each of the firing circuits 26, 27 and 28via a corresponding decoupling diode.

The charging capacitor C1 of the multivibrator can only charge duringperiods of time when none of the switching transistors of the differentfiring circuits 25, 26, 27 and 28 is controlled during the individualfiring stages. Thus, a sufficiently long charging period remains for thecapacitor C1 only at lower speeds of the motor to enable said capacitorto be charged to the magnitude of the firing or ignition voltage of thedouble base diode 58 in order to enable the initiation of the additionalfiring pulses. Two successive periods of time when a charging of thecapacitor C1 is possible are shown in FIG. 3 as t It is clear thatthrough appropriate selection of the charge time constants of thecapacitor 56 and the corresponding capacitors of the firing circuits 26,27 and 28, the charge time constant R1, Cl which determines thefrequency of oscillation of the multivibrator circuit may be keptsubstantially as low as desired. This is of advantage in avoidingcommutation short-circuits and thereby providing considerable smoothnessin the running of the motor.

While the invention has been described by means of specific examples andin specific embodiments, we do not wish to be limited thereto, forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit and scope of the invention.

We claim:

1. A start circuit for a DC motor having a rotor, a thyristor,:commutator comprising a plurality of thyristors and firing circuitmeans coupled to the rotor of the motor and connected to said thyristorsfor conductively controlling said thyristors with control pulses inaccordance with the position of the rotor of the motor, said firingcircuit means including a plurality of firing transformers eachconnected to a corresponding one of said thyristors, a plurality ofswitching transistors each connected to a corresponding one of saidfiring transformers and control means coupled to the rotor of the motorand connected to the switching transistors for supplying control pulsesto the switching transistors during a starting period, said startcircuit comprising a pulse generator connected to the switchingtransistors of the'firing circuits for providing additional controlpulses for said switching transistors during the starting period.

2. A start circuit as claimed in claim 1, wherein each of the switchingtransistors of the firing circuit means has a control path and whereinsaid firing circuit means further comprises a plurality of inputtransistors each having a collector electrode connected to the controlpath of a corresponding one of said switching transistors and a baseelectrode connected to said pulse generator whereby the additionalcontrol pulses provided by said pulse generator are superimposed uponthe control'pulses supplied to the switching transistors via the inputtransistors.

3. A start circuit as claimed in claim 2, wherein the pulse generatorcomprises a switching transistor connected as the output stage thereofand connected in parallel to the collector electrode of each of saidinput transistors and the control path of each of said switchingtransistors is energized by the collector potential of the correspondinginput transistor.

4. A start circuit as claimed in claim 2, wherein the pulse generatorcomprises a source of direct voltage, a charging capacitor and aresistor connected in series circuit arrangement with the chargingcapacitor to the source of direct voltage, a discharge current pathconnected to a common point in the connection between the chargingcapacitor and the resistor, and a switching transistor connected as theoutput stage of said pulse generator and connected in parallel to thecollector electrode of each of said input transistors.

5. A start circuit as claimed in claim 2, wherein said pulse generatorincludes a switch for controlling the output of the additional controlpulses and a limit circuit coupled to the rotor of the motor andcontrolling the operation of said switch for discontinuing the output ofthe additional control pulses from said pulse generator via said switchin accordance with the rotary speed of the motor.

6. A start circuit as claimed in claim 4, wherein the discharge currentpath of the pulse generator comprises a double base diode which is firedby the voltage of the charging capacitor.

7. A start circuit as claimed in claim 4, wherein each of the switchingtransistors has a base electrode and an emitter-collector path andwherein said firing circuit means further comprises a plurality ofcapacitors each connected between the collector electrode of acorresponding one of the input transistors and the base electrode of acorresponding one of the switching transistors, and a plurality ofdecoupling diodes each connected between the charging capacitor of thepulse generator and the emittencollector path of a corresponding one ofthe switching transistors.

8. A start circuit as claimed in claim 5, further comprising asine-cosine sensor having a pair of inputs coupled to the rotor of themotor and a pair of outputs and speed indicating means having inputscoupled to the outputs of the sine-cosine sensor and an output connectedto the limit circuit of said pulse generator.

9. A start circuit as claimed in claim 8, wherein said speed indicatingmeans comprises a first differentiator 14 having an input connected toone of said inputs, a first multiplier having an input connected inseries circuit arrangement with the first differentiator, another inputconnected to another of said inputs and an output, a seconddifferentiator having an input connected to the other of said inputs, asecond multiplier having an input connected in series circuitarrangement with the second differentiator, another input connected tothe first of said inputs and an output, and summing means having anoutput connected to the limit circuit of said pulse generator, an inputconnected to the output of the first multiplier and another inputconnected to the output of the second multiplier for subtractivelycombining output signals from said first and second multipliers.

10. A start circuit as claimed in claim 9, further comprising motorenergizing means connected between the output of said speed indicatingmeans and the thyristors of the thyristor commutator, said motorenergizing means including rectifier means connected to said thyristorsand a rectifier control unit connected to said rectifier means andhaving a synchronizing stage connected to said pulse generator forenergizing said pulse generator.

1. A start circuit for a DC motor having a rotor, a thyristor commutatorcomprising a plurality of thyristors and firing circuit means coupled tothe rotor of the motor and connected to said thyristors for conductivelycontrolling said thyristors with control pulses in accordance with theposition of the rotor of the motor, said firing circuit means includinga plurality of firing transformers each connected to a corresponding oneof said thyristors, a plurality of switching transistors each connectedto a corresponding one of said firing transformers and control meanscoupled to the rotor of the motor and connected to the switchingtransistors for supplying control pulses to the switching transistorsduring a starting period, said start circuit comprising a pulsegenerator connected to the switching transistors of the firing circuitsfor providing additional control pulses for said switching transistorsduring the starting period.
 2. A start circuit as claimed in claim 1,wherein each of the switching transistors of the firing circuit meanshas a control path and wherein said firing circuit means furthercomprises a plurality of input transistors each having a collectorelectrode connected to the control path of a corresponding one of saidswitching transistors and a base electrode connected to said pulsegenerator whereby the additional control pulses provided by said pulsegenerator are superimposed upon the control pulses supplied to theswitching transistors via the input transistors.
 3. A start circuit asclaimed in claim 2, wherein the pulse generator comprises a switchingtransistor connected as the output stage thereof and connected inparallel to the collector electrode of each of said input transistorsand the control path of each of said switching transistors is energizedby the collector potential of the corresponding input transistor.
 4. Astart circuit as claimed in claim 2, wherein the pulse generatorcomprises a source of direct voltage, a charging capacitor and aresistor connected in series circuit arrangement with the chargingcapacitor to the source of direct voltage, a discharge current pathconnected to a common point in the connection between the chargingcapacitor and the resistor, and a switching transistor connected as theoutput stage of said pulse generator and connected in parallel to thecollector electrode of each of said input transistors.
 5. A startcircuit as claimed in claim 2, wherein said pulse generator includes aswitch for controlling the output of the additional control pulses and alimit circuit coupled to the rotor of the motor and controlling theoperation of said switch for discontinuing the output of the additionalcontrol pulses from said pulse generator via said switch in accordancewith the rotary speed of the motor.
 6. A start circuit as claimed inclaim 4, wherein the discharge current path of the pulse generatorcomprises a double base diode which is fired by the voltage of thecharging capacitor.
 7. A start circuit as claimed in claim 4, whereineach of the switching transistors has a base electrode and anemitter-collector path and wherein said firing circuit means furthercomprises a plurality of capacitors each connected between the collectorelectrode of a corresponding one of the input transistors and the baseelectrode of a corresponding one of the switching transistors, and aplurality of decoupling diodes each connected between the chargingcapacitor of the pulse generator and the emitter-collector path of acorresponding one of the switching transistors.
 8. A start circuit asclaimed in claim 5, further comprising a sine-cosine sensor having apair of inputs coupled to the rotor of the motor and a pair of outputsand speed indicating means having inputs coupled to the outputs of thesine-cosine sensor and an output connected to the limit circuit of saidpulse generator.
 9. A start circuit as claimed in claim 8, wherein saidspeed indicating means comprises a first differenTiator having an inputconnected to one of said inputs, a first multiplier having an inputconnected in series circuit arrangement with the first differentiator,another input connected to another of said inputs and an output, asecond differentiator having an input connected to the other of saidinputs, a second multiplier having an input connected in series circuitarrangement with the second differentiator, another input connected tothe first of said inputs and an output, and summing means having anoutput connected to the limit circuit of said pulse generator, an inputconnected to the output of the first multiplier and another inputconnected to the output of the second multiplier for subtractivelycombining output signals from said first and second multipliers.
 10. Astart circuit as claimed in claim 9, further comprising motor energizingmeans connected between the output of said speed indicating means andthe thyristors of the thyristor commutator, said motor energizing meansincluding rectifier means connected to said thyristors and a rectifiercontrol unit connected to said rectifier means and having asynchronizing stage connected to said pulse generator for energizingsaid pulse generator.